This invention relates to improved powder paints and more particularly to ultraviolet curable powder paints produced from specific spatial arrangements of epoxy-polyester polymers.
Powder paints are ordinarily manufactured from raw batch ingredients comprising resinous binders, pigmentary solids, plasticizers, and other additives to provide good film properties and adhesion to substrates. The raw batch ingredients are uniformly mixed, formed into a coherent extrudate by hot extrusion and then comminuted to form small particle powder paints which are ordinarily free flowing at normal room temperature. Powder paints ordinarily are uniform powders less than about 325 mesh and can be effectively pigmented and expediently processed without contaminating process equipment such as suggested in commonly assigned U.S. Pat. No. 3,941,315 and the disclosure thereof is incorporated herein by reference. Powder paints contain little or no fugitive solvents and must depend upon their own inherent characteristics of the powder to level, coalesce and form an attractive coherent film on the substrate. The powder, however, must not fuse in the container or be subjective to cold flow and must maintain individual powder particles prior to application.
It now has been found that ethylenically unsaturated polymers having pendant acrylic unsaturation or similar ethylenic unsaturation can be effectively cured with ultraviolet energy provided the resinous binder for powder paints has a specific spatial arrangement of an epoxy-polyester polymer. The epoxy-polyester binder is sufficiently crystalline to resist cold flow but surprisingly provides excellent flow out at melting temperatures wherein such flow out could not be obtained by either an epoxy or a polyester polymer nor a blend of epoxy and polyester polymers. The epoxy-polyester polymer of this invention softens and flows out uniformly over a narrow melt temperature whereby the polymer can be efficiently cured by ultraviolet irradiation. The ultraviolet cured and cross-linked film exhibits excellent hardness, desirable flexibility, and excellent methyl ethyl keton (MEK) resistance.
These and other advantages will become more apparent by referring to the Detailed Description of the Invention.